Method for forming capacitor of semiconductor device

ABSTRACT

Disclosed is a method for forming a capacitor of a semiconductor device, which can secure wanted charging capacity and also improve leakage current characteristics. The method comprises the steps of: forming a storage electrode on a semiconductor substrate; forming a dielectric layer formed of Ti (1-x) Tb x O on the storage electrode; and forming a plate electrode on the dielectric layer formed of Ti (1-x) Tb x O.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for forming a capacitor of asemiconductor device, and more particularly to a method for forming acapacitor of a semiconductor device, which can sufficiently securenecessary charging capacity and also improve current leakage preventioncharacteristics.

2. Description of the Prior Art

Recently, as the high integration of a memory product accelerates due tothe development of the semiconductor process technology, the unit cellarea decreases and the operation voltage lowers. However, in spite ofthe decrease of the cell area, there has been continuous demands for amemory device having a sufficiently high charging capacity of at least25 fF per cell for the operation thereof, in order to prevent thegeneration of soft error and the reduction of refresh time.

Therefore, in case of a NO (Nitride Oxide) capacitor for DRAM whichemploys a dielectric body formed of an Si₃N₄ dielectric layer depositedby using DCS (Di-Chloro-Silane) gas, a charge storage electrode of threedimensional shape which has an electrode surface of semi-spherical shapehaving a wide surface area is used, and the height thereof continuouslyincreases in order to secure a sufficient capacity.

On the other hand, the NO capacitor shows a limit in securing a chargingcapacitance of over 256M needed for a next-generation DRAM product.Therefore, as shown in FIG. 1, capacitors employing a single dielectriclayer 5 made from a high dielectric material such as Ta₂O₅ (ε=25), Al₂O₃(ε=9), and HfO₂ (ε=20) have been actively developed in order to secure asufficient capacity. Recently, capacitors using an La₂O₃ (ε=27)dielectric layer are also being developed.

In FIG. 1, the reference numeral 1 represents a semiconductor substrate,2, an isolation interlayer, 3, a storage node contact, 4, a storageelectrode, and 5, a plate node.

However, since the dielectric constant of an Al₂O₃ dielectric layer isnot very large, there is a limit in securing the charge capacitance bythe Al₂O₃ dielectric layer. In HfO₂ and La₂O₃ dielectric layers whosedielectric constant are larger than that of the Al₂O₃ dielectric layer,if the equivalent SiO₂ thickness of the capacitor is lowered to about 15Å, the leakage current rapidly increases and the yield electric fieldstrength dramatically lowers. As a result, the layers are vulnerable torepetitive electric impacts and the endurance of the capacitordeteriorates.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made to solve theabove-mentioned problems occurring in the prior art, and an object ofthe present invention is to provide a method for forming a capacitor ofa semiconductor device, which can secure necessary charging capacity andalso improve current leakage prevention characteristics.

In order to accomplish the object, according to the present invention,there is provided a method for forming a capacitor of a semiconductordevice, which includes the steps of: forming a storage electrode on asemiconductor substrate; forming a dielectric layer formed ofTi_((1-x))Tb_(x)O on the storage electrode; and forming a plateelectrode on the dielectric layer formed of Ti_((1-x))Tb_(x)O.

Here, the storage electrode is formed by using a metal selected from thegroup consisting of doped poly-silicon (poly-Si), TiN, TaN, W, WN, WSi,Ru, RuO₂, Ir, IrO₂, and Pt.

A washing process is performed between the steps forming the dielectricelectrode and the plate electrode.

The washing process is performed by using an HF mixed solution includingH₂O and HF with a ratio of 10 to 100 for H₂O/HF or including NH₄F and HFwith a ratio of 5 to 500 for NH₄F/HF in order to remove a native oxidelayer.

After HF washing process, an additional washing process is performed byusing NH₄OH mixed solution (NH₄OH+H₂O₂+H₂O) or H₂SO₄ mixed solution(H₂SO₄+H₂O, H₂SO₄+H₂O).

Annealing is performed in an NH3 atmosphere to nitrify a surface of thestorage electrode.

The annealing is performed in a mixed gas of O₂ and N₂ mixed at a ratioless than 0.1 for O₂/N₂ at a temperature of 500 to 900° C. within afurnace under atmospheric pressure or vacuumed pressure with a flow rateof 1 to 10 slm or through a rapid heat-processing process.

The dielectric layer uses Ti(OCH(CH₃)₂)₄ which is a source gas having aTi component or an organic metallic composition containing Ti is used asa precursor, and one selected from the group consisting of O₃, O₂,plasma O₂, N₂O, and plasma N₂O or H₂O of a density of 200±20 g/m³ isused as the reaction gas.

The reaction gas flows at a rate of 0.1 to 1 slm.

The dielectric layer uses Tb(OC₂H₅)₃ which is a source gas having a Tbcomponent or an organic metallic composition containing Tb such asTb(CH₃)₃ is used as a precursor, and one selected from the groupconsisting of O₃, O₂, plasma O₂, N₂O, and plasma N₂O or H₂O of a densityof 200±20 g/m is used as the reaction gas.

The source gas flows at a rate of 50 to 500 sccm, and the reaction gasflows at a rate of 0.1 to 1 slm.

The dielectric layer contains Tb of 3 to 15%.

The plate electrode is formed by using a metal selected from the groupconsisting of doped poly-silicon (poly-Si), TiN, TaN, W, WN, WSi, Ru,RuO₂, Ir, IrO₂, Pt, etc.

In case that a metallic material is used as the material of the plate, asilicon nitride layer or a doped poly-silicon layer having the thicknessof 200 to 100 Å is formed on an upper portion of the plate electrode asan absorbing layer or a protecting layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be more apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a cross-sectional view of a capacitor for explaining a problemin a conventional method for forming a capacitor of a semiconductordevice;

FIGS. 2A to 2C are cross-sectional views of a capacitor for explaining amethod for forming a capacitor of a semiconductor device according to apreferred embodiment of the present invention; and

FIG. 3 is a view for showing formation of a dielectric layer followingan ALD or pulsed CVD process according to a preferred embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention will be described with reference toaccompanying drawings.

FIGS. 2A to 2C are cross-sectional views of a capacitor for explaining amethod for forming a capacitor of a semiconductor device according to apreferred embodiment of the present invention.

As shown in FIG. 2A, an isolation interlayer 12 is formed on an entireupper surface of the semiconductor substrate 11 on which a predeterminedlower pattern (not shown) including a transistor and a bitline isformed, so that the isolation interlayer 12 covers the lower patterns.Then, the isolation interlayer 12 is etched to form a contact holeexposing a substrate bonding area or a landing plug poly, and aconductive layer is then filled in the contact hole to form a contactplug, i.e., a storage0 node contact 13. Thereafter, doped poly-silicon(poly-Si) or a metallic material such as TiN, TaN, W, WN, WSi, Ru, RuO₂,Ir, IrO₂ or Pt is deposited on the isolation interlayer 12 and is thenpatterned, so that a storage electrode 14 connected to the storage nodecontact 13 is formed on the isolation interlayer 12.

Here, although FIG. 2A shows a storage electrode 14 having a cylindricalstructure, the storage electrode 14 may have a simple plate structure ora concave structure. Further, in case that the storage electrode 10 isformed of the doped poly-silicon, HSG (Hemi-Spherical Grain) may beformed on the surface thereof in order to secure a larger chargingcapacitance.

As shown in FIG. 2B, before the dielectric layer is formed, the nativeoxide layer on the storage electrode is removed and a washing process isperformed for hydrogen terminate simultaneously. Then, in case that thestorage electrode 14 is deposited with the doped poly-silicon, thesurfaces of the storage electrode 14 and the isolation interlayer 12 arewashed with an HF mixed solution with a mixing ratio, H₂O/HF of 10 to100 or NH₄F/HF of 5 to 500.

When it is necessary to remove inorganic or organic particles and otherforeign substances on the storage electrode, an additional washingprocess is performed by using NH₄OH mixed solution (NH₄OH+H₂O₂+H₂O) orH₂SO₄ mixed solution (H₂SO₄+H₂O₂, H₂SO₄+H₂O) after the HF washingprocess.

Thereafter, the dielectric layer 15 is formed of Ti_((1-x))Tb_(x)OTi_((1-x))Tb_(x)O (0.03≦x≦0.3) on the isolation interlayer 12 includingthe storage electrode 10 according to atomic layer deposition(hereinafter, referred to as ALD), pulsed chemical vapor deposition(hereinafter, referred to as pulsed CVD), and low pressure chemicalvapor deposition (hereinafter, referred to as LP CVD).

Then, when forming the dielectric layer 15, Ti(OCH(CH₃)₂)₄ which is asource gas having a Ti component or an organic metallic compositioncontaining Ti is used as a precursor, and one selected from the groupconsisting of O₃, O₂, plasma O₂, N₂O, and plasma N₂O or H₂O of a densityof 200±20 g/m³ is used as the reaction gas. Here, the reaction gas flowsat a rate of 0.1 to 1 slm (standard liters per minute).

Further, when forming the dielectric layer 15, Tb(OC₂H₅)₃ which is asource gas having Tb components or an organic metallic compositioncontaining Tb such as Tb(CH₃)₃ is used as a precursor, and one selectedfrom the group consisting of O₃, O₂, plasma O₂, N₂O, and plasma N₂O orH₂O of a density of 200±20 g/m³ is used as the reaction gas. Here, thesource gas flows at a rate of 50 to 500 sccm, and the reaction gas flowsat a rate of 0.1 to 1 slm.

As shown in FIG. 2C, a plate electrode 16 which uses one selected fromthe group consisting of doped silicon, TiN, TaN, W, WN, WSi, Ru, RuO₂,Ir, IrO₂, Pt, etc. is formed on the dielectric layer 15 formed ofTi_((1-x))Tb_(x)O to form a capacitor to which Ti_((1-x))Tb_(x)Odielectric layer according to the present invention is applied.

Here, in case that a metallic material is used as the material of theplate 16, a silicon nitride layer (SiN) or a doped poly-silicon layerhaving a thickness of 200 to 100 Å is formed on the upper portion of theplate electrode as an absorbing layer or a protecting layer to securethe structural safety from humidity, temperature, or electrical impact.

According to the present invention, it is preferred that, in the casethat the doped poly-silicon layer is applied as the material of thestorage electrode 14 or the plate electrode 16, a diffusion preventinglayer of SiN_(x) is formed on the surface of the storage electrodebefore forming the Ti_((1-x))Tb_(x)O dielectric layer and on the surfaceof the Ti_((1-x))Tb_(x)O dielectric layer lest silicon or dopants shouldbe penetrated towards the Ti_((1-x))Tb_(x)O dielectric layer. Here, inorder to form the diffusion preventing layer of SiN_(x), annealing isperformed in an NH3 atmosphere, and the surface of the storage electrodeand the surface of the Ti_((1-x))Tb_(x)O dielectric layer are nitrified;The annealing is performed in mixed gas of O₂ and N₂ mixed at a ratioless than 0.1 for O₂/N₂ at a temperature of 500 to 900° C. within afurnace under atmospheric pressure or vacuumed pressure with a flow rateof 1 to 10 slm or through a rapid heat-processing process.

FIG. 3 is a view for showing a dielectric layer forming processaccording to an ALD or pulsed CVD process according to a preferredembodiment of the present invention.

As shown in FIG. 3, the Ti_((1-x))Tb_(x)O dielectric layer is formed bysequentially processing the steps of flowing of source gas (Ti or Tb),purging, flowing of reaction gas (O₃), and purging and repetitivelyperforming the sequential processes until a wanted thickness isobtained. Then, the Ti_((1-x))Tb_(x)O dielectric layer is formed withthe formation rate of TiO₂ to Tb_(x)O_(y) being nine to one. Further,the Ti_((1-x))Tb_(x)O dielectric layer can be formed by sequentiallyprocessing the steps of flowing of source gas (Ti), purging, flowing ofsource gas (Tb), purging, flowing of reaction gas (O₃), and purging andrepetitively performing the sequential processes until a wantedthickness is obtained. Then, the Ti_((1-x))Tb_(x)O dielectric layerhaving a mixed phase is formed by first forming a amorphous dielectriclayer of under 100 Å while regulating the number of times of theinjections of the Tb source gas with the formation rate of TiO₂ toTb_(x)O_(y) being under seven to three and then by performing annealingat a temperature of 500 to 800° C.

In forming the dielectric layer according to the LP CVD process, Ti andTb are injected through a flow rate regulating device respectively,through evaporators or evaporating tubes maintained at a constanttemperature with the ratio of Ti to Tb being under 7:3. Then, the sourcegas of the Ti component and the source gas of the Tb component areinjected respectively into a chamber of 250 to 500 degrees Celsius toform the Ti_((1-x))Tb_(x)O dielectric layer of under 100 Å.

As is mentioned above, according to the present invention, by formingthe Ti_((1-x))Tb_(x)O dielectric layer on the storage electrode of dopedsilicon or a metallic material, the charging capacitance needed in aDRAM product of under 100 nm is secured and the leakage current andyield voltage characteristics are controlled so as to have a level ofmass-production of under 0.5 fA and over 7 MV/cm, and thereby theendurance and the electrical efficiency of the capacitor can improvesimultaneously.

Although a preferred embodiment of the present invention has beendescribed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. A method for forming a capacitor of a semiconductor device, whichcomprises the steps of: forming a storage electrode on a semiconductorsubstrate; forming a dielectric layer formed of Ti_((1-x))Tb_(x)O on thestorage electrode; and forming a plate electrode on the dielectric layerformed of Ti_((1-x))Tb_(x)O.
 2. A method according to claim 1, whereinthe storage electrode is formed by using a metal selected from the groupconsisting of doped poly-silicon (poly-Si), TiN, TaN, W, WN, WSi, Ru,RuO₂, Ir, IrO₂, and Pt.
 3. A method according to claim 1, wherein awashing process is performed between the steps forming the dielectricelectrode and the plate electrode.
 4. A method according to claim 3,wherein the washing process is performed by using an HF mixed solutionincluding H₂O and HF with a ratio of 10 to 100 for H₂O/HF or includingNH₄F and HF with a ratio of 5 to 500 for NH₄F/HF in order to remove anative oxide layer.
 5. A method according to claim 3, wherein, after HFwashing process, an additional washing process is performed by usingNH₄OH mixed solution (NH₄OH+H₂O₂+H₂O) or H₂SO₄ mixed solution(H₂SO₄+H₂O₂, H₂SO₄+H₂O).
 6. A method according to claim 3, whereinannealing is performed in an NH3 atmosphere to nitrify a surface of thestorage electrode.
 7. A method according to claim 6, wherein theannealing is performed in a mixed gas of O₂ and N₂ mixed at a ratio lessthan 0.1 for O₂/N₂ at a temperature of 500 to 900° C. within a furnaceunder atmospheric pressure or vacuumed pressure with a flow rate of 1 to10 slm or through a rapid heat-processing process.
 8. A method accordingto claim 1, wherein the dielectric layer uses Ti(OCH(CH₃)₂)₄ which is asource gas having a Ti component or an organic metallic compositioncontaining Ti is used as a precursor, and one selected from the groupconsisting of O₃, O₂, plasma O₂, N₂O, and plasma N₂O or H₂O of a densityof 200±20 g/m³ is used as the reaction gas.
 9. A method according toclaim 8, wherein the reaction gas flows at a rate of 0.1 to 1 slm.
 10. Amethod according to claim 1, wherein the dielectric layer usesTb(OC₂H₅)₃ which is a source gas having a Tb component or an organicmetallic composition containing Tb such as Tb(CH₃)₃ is used as aprecursor, and one selected from the group consisting of O₃, O₂, plasmaO₂, N₂O, and plasma N₂O or H₂O of a density of 200±20 g/m³ is used asthe reaction gas.
 11. A method according to claim 10, wherein the sourcegas flows at a rate of 50 to 500 sccm, and the reaction gas flows at arate of 0.1 to 1 slm.
 12. A method according to claim 1, wherein thedielectric layer contains Tb of 3 to 15%.
 13. A method according toclaim 1, wherein the plate electrode is formed by using a metal selectedfrom the group consisting of doped poly-silicon (poly-Si), TiN, TaN, W,WN, WSi, Ru, RuO₂, Ir, IrO₂, Pt, etc.
 13. A method according to claim 1,wherein, in case that a metallic material is used as the material of theplate, a silicon nitride layer or a doped poly-silicon layer having athickness of 200 to 100 Å is formed on an upper portion of the plateelectrode as an absorbing layer or a protecting layer.